[TASK] Use register attribute in Collector (#686)

TYPO3 v14 remodels TypoScript 'register' handling. The
patch adds this to the FE testing related Collector
class with a fallback layer for earlier TYPO3 versions.

Related: https://forge.typo3.org/issues/107625

Author: lolli42

Classes/Core/Functional/Framework/Frontend/Collector.php

@@ -142,12 +142,13 @@ private function getTableFields(string $tableName, ServerRequestInterface $reque
 
     private function getCurrentWatcherValue(ServerRequestInterface $request): ?string
     {
-        $watcherValue = null;
-        $tsfe = $request->getAttribute('frontend.controller');
-        if (isset($tsfe->register['watcher'])) {
-            $watcherValue = $tsfe->register['watcher'];
+        $registerStack = $request->getAttribute('frontend.register.stack');
+        if ($registerStack !== null) {
+            return $registerStack->current()->get('watcher');
         }
-        return $watcherValue;
+        // @deprecated: TYPO3 <v14 b/w compat. Remove $tsfe fallback and if clause above when v13 compat is removed.
+        $tsfe = $request->getAttribute('frontend.controller');
+        return $tsfe->register['watcher'] ?? null;
     }
 
     private function getRenderer(): Renderer